Vending machines in the field include interior fluorescent lamps that illuminate a large front panel typically having a sign advertising the items available for vending. These illuminated vending machines attract consumers. But studies show that vending machine sales drop off dramatically when one or more of the lamps go out because customers perceive that the vending machine is broken. Thus, there is a need for a device to alert the vending machine owner when one or more of the lamps are showing signs of failing.